Hermetically sealed coaxial connector



Sept. 11, 1956 A. CHLAVIN 2,762,991

HERMETICALLY SEALED COAXIAL CONNECTOR Filed July 6, 1954 a liza- 2 A W/ZA Z'fl/K /4z/ //z/ a/zm w,

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lifdlA l United States Patent Alvin Chlavin, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application July 6, 1954, Serial No. 441,286 4 Claims. (Cl. 339-177) This invention relates to coaxial connectors, and more particularly to means for providing, and methods of producing, a glass-to-metal hermetic seal for miniature coaxial cables.

In general, the requirements for hermetically sealed connectors include, amongst others, proper insulation, proper electrical contacts, proper hermetic seals, proper protection against damage in handling, and proper materials unaffected by environmental conditions. These requirements are conventionally met and satisfied by the use of metal conductors and glass insulators which have the same coefiicient of expansion. However, in attempting to develop a reliable hermetically sealed connector for bringing miniature coaxial cables into or out of hermetically sealed enclosures, an important problem, and one which has not been satisfactorily solved, is that of providing good electrical contact pressure and sufiicient mechanical support between the coaxial cable and the coaxial connector. This is particularly difficult if the connector is flush-mounted and the center conductor of the coaxial cable has a diameter of less than one thirtysecond of an inch, because such a small center conductor does not lend itself to such operations as slotting or threading, as in the case of large conductors, to adapt it to be satisfactorily supported by the connector.

Accordingly, it is one of the objects of this invention to provide a hermetically sealed coaxial connector which is capable of holding a miniature center conductor of a coaxial cable in releasable engagement to provide mechanical support and electrical contact pressure between the center conductor and the connector.

It is a further object of this invention to provide a hermetically sealed coaxial connector arrangement which can releasably engage a miniature coaxial cable with sufficient force to insure good mechanical support for and electrical contact pressure with the cable, without any possibility of damage to the cable.

It is a further object of this invention to provide a method of manufacturing a hermetically sealed coaxial connector using a selective etch process which is particularly applicable to coaxial cables having center condoctors of small diameter.

A preferred embodiment of this invention is a hermetically sealed coaxial connector having inner and outer conductors separated by glass, where the glass has the same coefficient of expansion as the conductors. The center conductor of the connector contains an opening of the size of the center conductor of the coaxial cable to be received. The center conductor of the connector is further provided with at least one cross-cut which extends throughout the length of the opening. The end of the center conductor containing this cross-cut is slightly crimped to provide spring action to releasably engage the center conductor. To prevent the spring action from exerting any pressure on the glass walls of the insulator, the glass insulator is relieved or recessed around the inner conductor for the length of the cross-cut. This recess provides enough space to accommodate any motion of the inner conductor upon insertion of the center conductor of the coaxial cable, thereby to prevent contact between the glass seal and the center conductor of the connector.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings, in which a preferred embodiment of the invention is illustrated by way of example. it is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. l is a sectional view in elevation of the hermetically sealed coaxial connector in accordance with this invention; and

Fig. 2 is a cross-sectional view taken across the line 2-2 of Fig. 1.

Referring to the drawings, which are made part of the specification, like reference characters are used to indicate like parts throughout. Figs. 1 and 2 show the hermetically sealed coaxial connector which is inserted into a suitable circular opening in the enclosure to be sealed hermetically, as by soldering the connector into the rest of the enclosure in a manner well established in the prior art.

A conductor ring it and center conductor 11 form the outer and center conductor of a coaxial connector, respectively. Outer conductor 10 is placed about the periphery of a cast glass cylinder 12 which forms a hermetic seal. Center conductor 11 extends through the center of glass cylinder 12. A cylindrical opening 13 in the end of center conductor 11 is provided to receive the center conductor of the coaxial cable which is to be admitted into the hermetically sealed enclosure. Further, a slit or cross-cut 14 is provided in the center conductor 11 for the purpose of furnishing spring action contact when the center conductor of the coaxial cable is inserted. This is accomplished by slightly crimping together the contact ends 15 of center conductor 11. A relief or recess 16 in the glass cylinder 12 about center conductor 11 extends into glass cylinder 12 to a depth approximately equal to that of the cross-cut 14. Recess 16 provides space into which the contact ends 15 can move when the center conductor of the coaxial cable is inserted into the opening 13. This will prevent the contact ends 15 from subjecting the cast glass 12 to any strain which might result in the breaking of the hermetic seal and allows for spring contact for electrical connection.

The method by which the connector of Fig. 1 is manufactured is as follows: for the outer and center conductors lit and 11, respectively, a metal and glass are selected which have substantially the same coetficient of expansion as the glass cylinder. A typical example of a suitable metal is that known as Kovar, which is an alloy containing 20% nickel, 17% cobalt, 0.2% manganese, and the balance iron. Any suitable glass, such as glass having a Corning number 752, may be selected which has the same coefficient of expansion. The center conductor 11 is provided with the opening 13 and a cross-cut 14 as described above. Both the outer conductor and the center conductor are then rodium plated to make them impervious to attack by nitric acid which is part of this process. The contact ends 15 formed by the cross-cut 14 are then slightly crirnped together. The opening 13 and cross-cut 14 are then plugged up with a mating part which completely fills the opening and the cross-cut. Such mating part would conveniently be provided with means to effect its removal at a later time from the center conductor 11; such means could be excess material to provide a convenient grip.

The exterior of the inner conductor is nickel plated coextensive with the cross-cut to the length of the crosscut. The thickness of the nickel plate is equal to the width of the desired recess 16 to provide space for the spring action of the contact ends 15. Thereafter, the

glass is cast between the outer conductor and the inner conductor 11 by methods well-known to the prior art. When the glass is solidified, the entire assembly is submerged in nitric acid, which attacks the nickel plating and dissolves it completely, thereby creating the cylindrical recess 16. At the same time, the mating plug is freed from the glass seal. Thereafter, the mating plug is removed.

'What is claimed is:

l. A hermetically sealed coaxial connector comprising an outer conductor, a center conductor, and a dielectric support, said outer conductor being a short, hollow cylindrical section, and said center conductor being a cylindrical section of substantially smaller diameter than the inside diameter of said outer conductor, said center conductor having a central opening at one end thereof, said central opening extending partially into said center conductor, said center conductor having at least one thin cross-cut in a plane which passes through the axis of center conductor, said cross-cut being coextensive with said opening, said outer conductor and said center conductor being supported in concentric relation by said dielectric support, said dielectric support providing a hermetic seal with said outer and center conductors, said dielectric support having a small cylindrical relief coaxial and immediately adjacent to said center conductor and coextensive with said cross-cuts, said outer conductor, center conductor, dielectric support, all having the same coeflicient of expansion.

2. The process of fabricating a hermetically sealed coaxial connector having concentric inner and outer conductors, wherein the portion of the inner conductor which is concentric with the outer conductor is hollow, said process comprising the steps of providing at least one cross cut through the walls of said hollow portion of the inner conductor, rodiurn plating said inner and'outer conductors, nickel plating said center conductor coextensive with the hollow portion of said inner conductor,

plugging up said hoilow portion and said cross-cut, filling the space between the concentrically spaced outer and inner conductors with molten glass which, when solidified, will have the same coefiicient of expansion as said inner conductor, permitting the glass to solidify, and submerging the entire assembly in nitric acid to remove the nickel plating to provide an air relief around said hollow portion of the inner conductor.

3. A hermetically sealed coaxial connector for holding a miniature center conductor to a coaxial cable in releasable engagement comprising an outer conductor, a center conductor, and a dielectric seal, said outer conductor being an elongated ring, and said center conductor being a short cylinder having a central opening Whose diameter is the same as said miniature center conductor, said center conductor having at least one diameter crosscut, said cross-cut being coextensive with said opening, said outer and center conductors being supported in spaced concentric relation by said dielectric seal, said dielectric seal being recessed adjacent to said center conductor and coextensive with said opening, said recess having a radial dimension at least equal to any radial motions of the center conductor due to the cross-cut expansion of releasable engagement.

4. A method for producing a hermetically sealed coaxial connector having concentric outer and center conductors, said method comprising the steps of providing a cross-cut in one end of said center conductor, rodium plating the outer and the center conductors, nickel plating said center conductor coextensive With said crosscut, plugging up said center conductor and the cross-cut therein, filling the space between the concentric inner and outer conductors with molten glass, permitting the glass to solidify, submerging said connector with said solidified glass into nitric acid to remove the nickel plating and thereby providing a recess in said glass around said one end of the center conductor.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,737 Browne Oct. 14, 1941 2,508,018 Ellwood May 16, 1950 2,544,430 McCutchan Mar. 6, 1951 2,548,457 Wilson Apr. 10, 1951 

